1. Technical Field
The invention relates generally to integrated circuit (IC) chip fabrication, and more particularly, to a heterojunction bipolar transistor (HBT) with a monocrystalline base and emitter and methods related thereto.
2. Background Art
Silicon germanium (SiGe) heterostructure bipolar transistors (HBT) are high performance transistor structures used widely in high-speed integrated circuit (IC) chips. Advancement of SiGe HBT technology, however, is hindered by a number of challenges. For example, to meet costumer demands and market trends toward higher speeds and lower power consumption, devices are scaled, i.e. reduced in size. Consequently, small lithographic printing dimensions and the ability to align mask levels with extreme precision are required. Even small misalignments and device size increases result in performance degradation due to increased overlap capacitances, even device failure. In addition, current high-performance HBT technologies are expected to exhibit a larger statistical spread in key parameters due to minute lithographic variations. These key parameters include, for example, base resistance (Rb), threshold frequency (Ft), maximum frequency (Fmax), etc. Conventionally, all of the regions of the HBT (e.g., emitter, collector, base) are generated using non-self-aligned photolithography techniques. These known approaches result in problems such as emitter and base mis-alignment and non-planarity, a discontinuous polycrystalline intrinsic base resulting in a polycrystalline extrinsic base, etc. As a result, high performance SiGe HBTs are becoming harder to fabricate because of issues related to advanced scaling of dimensions. In order to address the above-described problems and allow for future scaling of HBTs, self-alignment integration schemes are desired. Unfortunately, conventional self-alignment techniques are inadequate to address the above-described problems.